Résumé :
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In amniotes, all skeletal muscles of the body and the limbs derive from mesodermal embryonic structures, named the somites. We utilize the electroporation of fluorescent reporter genes (e.g. GFP) in somites of chick embryos, combined with video-confocal analysis to characterize the morphogenetic movements that underlie the formation of skeletal muscles during embryogenesis. Notably, this led us to identify the embryonic origin of a population of muscle progenitors that participates to the growth of all skeletal muscles of the embryo and of the fetus. Long-term lineage analyses show that satellite cells, the major muscle stem cells of the adult, derive from the same population. The rate of proliferation or of differentiation of muscle progenitors determines the final size of skeletal muscles in the embryo. How is this size regulated is poorly understood. We have analyzed the role that myostatin (a TGF-? family member, and an important regulator of adult muscle size) plays during chick and mouse embryonic development. Our data show that myostatin acts in vivo to regulate the balance between proliferation and differentiation of embryonic muscle progenitors by promoting their terminal differentiation.
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